From: Tomasz Figa <tfiga@chromium.org>
To: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl>,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
Dan Carpenter <error27@gmail.com>,
oe-kbuild@lists.linux.dev, m.szyprowski@samsung.com,
mchehab@kernel.org, ming.qian@nxp.com, shijie.qin@nxp.com,
eagle.zhou@nxp.com, bin.liu@mediatek.com, matthias.bgg@gmail.com,
angelogioacchino.delregno@collabora.com,
tiffany.lin@mediatek.com, andrew-ct.chen@mediatek.com,
yunfei.dong@mediatek.com, stanimir.k.varbanov@gmail.com,
quic_vgarodia@quicinc.com, agross@kernel.org,
andersson@kernel.org, konrad.dybcio@linaro.org,
ezequiel@vanguardiasur.com.ar, p.zabel@pengutronix.de,
daniel.almeida@collabora.com, lkp@intel.com,
oe-kbuild-all@lists.linux.dev, linux-media@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-mediatek@lists.infradead.org,
linux-arm-msm@vger.kernel.org,
linux-rockchip@lists.infradead.org, kernel@collabora.com
Subject: Re: [PATCH v2 2/8] media: videobuf2: Make bufs array dynamic allocated
Date: Fri, 19 May 2023 10:00:24 +0000 [thread overview]
Message-ID: <20230519100024.en7immda3jdj2wwq@chromium.org> (raw)
In-Reply-To: <7ad524a1-c54f-a01c-3453-2cf1f0f82a13@collabora.com>
On Fri, Mar 24, 2023 at 09:56:34AM +0100, Benjamin Gaignard wrote:
>
> Le 24/03/2023 à 09:52, Hans Verkuil a écrit :
> > On 24/03/2023 09:48, Laurent Pinchart wrote:
> > > On Fri, Mar 24, 2023 at 09:31:35AM +0100, Hans Verkuil wrote:
> > > > On 24/03/2023 09:11, Benjamin Gaignard wrote:
> > > > > Le 24/03/2023 à 06:01, Dan Carpenter a écrit :
> > > > > > Hi Benjamin,
> > > > > >
> > > > > > https://git-scm.com/docs/git-format-patch#_base_tree_information]
> > > > > >
> > > > > > url: https://github.com/intel-lab-lkp/linux/commits/Benjamin-Gaignard/media-videobuf2-Access-vb2_queue-bufs-array-through-helper-functions/20230321-183154
> > > > > > base: git://linuxtv.org/media_tree.git master
> > > > > > patch link: https://lore.kernel.org/r/20230321102855.346732-3-benjamin.gaignard%40collabora.com
> > > > > > patch subject: [PATCH v2 2/8] media: videobuf2: Make bufs array dynamic allocated
> > > > > > config: arm64-randconfig-m041-20230319 (https://download.01.org/0day-ci/archive/20230324/202303240148.lKRnUqW9-lkp@intel.com/config)
> > > > > > compiler: aarch64-linux-gcc (GCC) 12.1.0
> > > > > >
> > > > > > If you fix the issue, kindly add following tag where applicable
> > > > > > | Reported-by: kernel test robot <lkp@intel.com>
> > > > > > | Reported-by: Dan Carpenter <error27@gmail.com>
> > > > > > | Link: https://lore.kernel.org/r/202303240148.lKRnUqW9-lkp@intel.com/
> > > > > >
> > > > > > smatch warnings:
> > > > > > include/media/videobuf2-core.h:1272 vb2_queue_add_buffer() warn: sleeping in atomic context
> > > > > > drivers/media/common/videobuf2/videobuf2-core.c:2456 vb2_core_queue_init() warn: Please consider using kcalloc instead of kmalloc_array
> > > > > >
> > > > > > vim +1272 include/media/videobuf2-core.h
> > > > > >
> > > > > > 625d46c1c1fe8e Benjamin Gaignard 2023-03-21 1263 static inline bool vb2_queue_add_buffer(struct vb2_queue *q, struct vb2_buffer *vb)
> > > > > > 625d46c1c1fe8e Benjamin Gaignard 2023-03-21 1264 {
> > > > > > 487d3f14d12ecf Benjamin Gaignard 2023-03-21 1265 bool ret = false;
> > > > > > 487d3f14d12ecf Benjamin Gaignard 2023-03-21 1266
> > > > > > 487d3f14d12ecf Benjamin Gaignard 2023-03-21 1267 spin_lock(&q->bufs_lock);
> > > > > > ^^^^^^^^^^^^^^^^^^^^^^^
> > > > > > Holding a spin lock.
> > > > > >
> > > > > > 487d3f14d12ecf Benjamin Gaignard 2023-03-21 1268
> > > > > > 487d3f14d12ecf Benjamin Gaignard 2023-03-21 1269 if (vb->index >= q->max_num_bufs) {
> > > > > > 487d3f14d12ecf Benjamin Gaignard 2023-03-21 1270 struct vb2_buffer **tmp;
> > > > > > 487d3f14d12ecf Benjamin Gaignard 2023-03-21 1271
> > > > > > 487d3f14d12ecf Benjamin Gaignard 2023-03-21 @1272 tmp = krealloc_array(q->bufs, q->max_num_bufs * 2, sizeof(*q->bufs), GFP_KERNEL);
> > > > > > ^^^^^^^^^^
> > > > > > Sleeping allocation. GFP_ATOMIC? Or is there a way to move the
> > > > > > allocation outside the lock?
> > > > > I will add GFP_ATOMIC flag in next version.
> > > > No need. Instead, don't use realloc here, just allocate a new array, copy over all
> > > > the data from the old, and then switch q->bufs with the spinlock held. Then you
> > > > can free the old one.
> > > >
> > > > It's only when you update q->bufs that you need the lock.
> > > The copy also needs to be protected by the lock.
> > I suspect that that is not needed, since you shouldn't be able to add buffers here
> > since a mutex should be held at this time.
> >
> > That said, it's something that Benjamin needs to analyze.
I spent some time looking through the call sites of vb2_get_buffer() and
how those can be called and it turned out to be a massive list of code
paths, including a lot of calls originating from codec drivers calling
vb2_find_buffer() in random contexts (possibly even interrupt). So a
spinlock protecting the array pointer makes sense indeed.
>
> Does using GFP_ATOMIC is problematic ?
>
Yes, because the ability to reclaim memory is drastically limited and
the allocation is more likely to fail (as in: it's actually possible).
(And generally the time with interrupts disabled should be minimized to
keep system latency reasonable.)
Best regards,
Tomasz
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next prev parent reply other threads:[~2023-05-19 11:01 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-21 10:28 [PATCH v2 0/8] Add DELETE_BUF ioctl Benjamin Gaignard
2023-03-21 10:28 ` [PATCH v2 1/8] media: videobuf2: Access vb2_queue bufs array through helper functions Benjamin Gaignard
2023-03-21 17:42 ` kernel test robot
2023-05-18 10:37 ` Tomasz Figa
2023-03-21 10:28 ` [PATCH v2 2/8] media: videobuf2: Make bufs array dynamic allocated Benjamin Gaignard
2023-03-21 18:16 ` Laurent Pinchart
2023-05-19 10:04 ` Tomasz Figa
2023-03-24 5:01 ` Dan Carpenter
2023-03-24 8:11 ` Benjamin Gaignard
2023-03-24 8:31 ` Hans Verkuil
2023-03-24 8:48 ` Laurent Pinchart
2023-03-24 8:52 ` Hans Verkuil
2023-03-24 8:56 ` Benjamin Gaignard
2023-05-19 10:00 ` Tomasz Figa [this message]
2023-03-24 13:02 ` Dmitry Osipenko
2023-03-21 10:28 ` [PATCH v2 3/8] media: videobuf2: Add a module param to limit vb2 queue buffer storage Benjamin Gaignard
2023-03-21 17:01 ` kernel test robot
2023-03-21 19:15 ` kernel test robot
2023-03-22 6:22 ` [EXT] " Ming Qian
2023-05-19 10:19 ` Tomasz Figa
2023-05-30 17:38 ` Laurent Pinchart
2023-05-31 6:36 ` Hans Verkuil
2023-05-31 8:03 ` Laurent Pinchart
2023-05-31 8:30 ` Hans Verkuil
2023-05-31 12:39 ` Laurent Pinchart
2023-06-01 8:03 ` Benjamin Gaignard
2023-06-01 8:34 ` Laurent Pinchart
2023-06-08 10:24 ` Tomasz Figa
2023-06-08 10:42 ` Laurent Pinchart
2023-03-21 10:28 ` [PATCH v2 4/8] media: videobuf2: Stop define VB2_MAX_FRAME as global Benjamin Gaignard
2023-05-23 7:14 ` Tomasz Figa
2023-03-21 10:28 ` [PATCH v2 5/8] media: v4l2: Add DELETE_BUF ioctl Benjamin Gaignard
2023-03-21 20:06 ` kernel test robot
2023-05-23 8:23 ` Tomasz Figa
2023-03-21 10:28 ` [PATCH v2 6/8] media: v4l2: Add mem2mem helpers for " Benjamin Gaignard
2023-03-21 10:28 ` [PATCH v2 7/8] media: vim2m: Use v4l2-mem2mem helpers for VIDIOC_DELETE_BUF ioctl Benjamin Gaignard
2023-03-21 10:28 ` [PATCH v2 8/8] media: verisilicon: " Benjamin Gaignard
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